Only thing quiet enough for no headsets is a turbine. Except the cost of the turbine alone is more than 250k LOL . So, I guess you could buy the new Breitling sponsored flying man suit....jk... But, in reality he has a lot of demands for what he's budgeting. Welcome to business and corporate, right? However, i'd say a non-pressurized Piper Navajo. It has A/C optional, and it has seating for 8 total plus a porta-potty option, or a 9th seat and no porta-potty... Insurance wise you'd probably have to have 2 pilots obviously with Commercial AMEL's. Throw the idea his way, see what he has to say. Otherwise, if you want a single...... i'll think on this one...